This application is related to concurrently filed and commonly assigned applications (serial numbers to be assigned) entitled:
xe2x80x9cMethod of Forming Cuxe2x80x94Caxe2x80x94O Thin Films on Cu Surfaces in a Chemical Solution and Semiconductor Device Thereby Formed;xe2x80x9d
xe2x80x9cMethod of Calcium Doping a Cu Surface Using a Chemical Solution and Semiconductor Device Thereby Formed;xe2x80x9d
xe2x80x9cMethod of Reducing Carbon, Sulphur, and Oxygen Impurities in a Calcium-Doped Cu Surface and Semiconductor Device Thereby Formed;xe2x80x9d
xe2x80x9cMethod of Reducing Electromigration in Copper Lines by Calcium-Doping Copper Surfaces in a Chemical Solution and Semiconductor Device Thereby Formed;xe2x80x9d and
xe2x80x9cMethod of Reducing Electromigration in Copper Lines by Forming an Interim Layer of Calcium-Doped Copper Seed Layer in a Chemical Solution and Semiconductor Device Thereby Formed.xe2x80x9d
The present invention relates to semiconductor devices and their methods of fabrication. More particularly, the present invention relates to the processing of copper interconnect material and the resultant device utilizing the same. Even more particularly, the present invention relates to reducing electromigration in copper interconnect lines by doping their surfaces with barrier material using wet chemical methods.
Currently, the semiconductor industry is demanding faster and denser devices (e.g., 0.05-xcexcm to 0.25-xcexcm) which implies an ongoing need for low resistance metallization. Such need has sparked research into resistance reduction through the use of barrier metals, stacks, and refractory metals. Despite aluminum""s (Al) adequate resistance, other Al properties render it less desirable as a candidate for these higher density devices, especially with respect to its deposition into plug regions having a high aspect ratio cross-sectional area. Thus, research into the use of copper as an interconnect material has been revisited, copper being advantageous as a superior electrical conductor, providing better wettability, providing adequate electromigration resistance, and permitting lower depositional temperatures. The copper (Cu) interconnect material may be deposited by CVD, PECVD, sputtering, electroless plating, and electrolytic plating.
However, some disadvantages of using Cu as an interconnect material include etching problems, corrosion, and diffusion into silicon.1 These problems have instigated further research into the formulation of barrier materials for preventing electromigration in both Al and Cu interconnect lines.
1Peter Van Zant, Microchip Fabrication: A Practical Guide to Semiconductor Processing, 3rd Ed., p. 397 (1997). 
In response to electromigration concerns relating to the fabrication of semiconductor devices particularly having aluminum-copper alloy interconnect lines, the industry has been investigating the use of various barrier materials such as titanium-tungsten (TiW) and titanium nitride (TiN) layers as well as refractory metals such as titanum (Ti), tungsten (W), tantalum (Ta), and molybdenum (Mo) and their silicides.2 Although the foregoing materials are adequate for Al interconnects and Alxe2x80x94Cu alloy interconnects, they have not been entirely effective with respect to all-Cu interconnects. Further, though CVD has been conventionally used for depositing secondary metal(s) on a primary metal interconnect surface, CVD is not a cost-effective method of doping Cu interconnect surfaces with calcium (Ca) ions. Therefore, a need exists for a nontoxic aqueous chemical solution for forming a Cuxe2x80x94Caxe2x80x94O thin film on a Cu surface in order to improve interconnect reliability, to enhance electromigration resistance, and to improve corrosion resistance.
Accordingly, the present invention provides a nontoxic aqueous chemical solution for forming a Cuxe2x80x94Caxe2x80x94O thin film on a Cu surface. Specifically, the present invention chemical solution is used to form a thin film which reduces electromigration in Cu interconnect lines by decreasing the drift velocity therein which decreases the Cu migration rate in addition to void formation rate. More specifically, the present invention provides a unique chemical solution for forming a copper-calcium-oxide (Cuxe2x80x94Caxe2x80x94O) thin film on a copper (Cu) surface, comprising: (a) at least one calcium (Ca) ion source for providing a plurality of Ca ions; (b) at least one complexing agent for complexing the plurality of Ca ions; (c) at least one copper (Cu) ion source for providing a plurality of Cu ions; (d) at least one complexing agent for complexing the plurality of Cu ions; (e) at least one pH adjuster; (f) at least one reducing agent for facilitating deposition of the plurality of Cu ions; (g) at least one wetting agent for stabilizing the chemical solution; and (h) a volume of water, (a) through (g) being dissolved in (h). The Cu surface may be immersed in the chemical solution for forming the Cuxe2x80x94Caxe2x80x94O thin film. By forming the Cuxe2x80x94Caxe2x80x94O thin film, the present invention improves interconnect reliability, enhances electromigration resistance, and improves corrosion resistance.